Rubber shoe sole



Au@ 5, 1941 w. L. SMITH I l 2,251,468

. RUBBER suon soLE Fiiea Apri; 5, v1959 I Il Y lNVENTO R Patented Aug. 5, 1941 RUBBER SHOE SOLE Wesley L. Smith, Bedford, Va., assignor, by mesne assignments, to Salta Corporation, N. J., a corporation of Delaware Jersey City,

Application April 5, 1939, Serial No. 266,155

, 3 Claims.

-This invention relates to rubber shoe soles, and

, aims to provide a sole having good wearing qualities and capable throughout its life of on smooth and wet surfaces.

gripping Inaccordance with my invention, a shoe sole is made from wholly or partially collapsed, 'closed-cell, cellular rubber. Such rubber is made by expanding a mass of soft rubber compound by means of a usual blowing agent under conditions which retain the gases produced by th'e blowing agent in closed cells Within'the mass ofv compound, and then cooling the rubber mass after vulcanization. The cooling has the eiect of condensing or otherwise eliminating the gases produced by the blowing agent, so that the soft vulcanized rubber collapses substantially to the volume whichy it had before expansion. In its collapsed "form, it has about the same degree of resiliency and the same wearing qualities of solid unexpanded soft rubber. Such collapsed-cellular rubberhas been `made as an intermediate product in making sponge rubber, but has generally been regarded as of no value in itself.

i have discovered that when shoe-soles are made of collapsed cellular rubber, they are resillent, strong and durable and have the property of gripping on smooth surfaces vuntil they are completely worn away. This property arises from the fact that wear on the under-surface of a sole made of collapsed cellular rubber opens the collapsed cells near the wearing surface, relieving the vacuum in these cells so that they expand and serve by' a-vacuum cup action to prevent the sole from slipping on smooth surfaces. ThusB a1- thougl'l the sole has only thenormal resiliency of solid soft rubber, its under-surface, as wear continues, consists always of -a thin layer of expanded rubber containing opened cells which serve as vacuumcups.

To prevent the 'sole from slipping 1when it is new, indentatlons .may be molded in tlile undersurface to provide an initial. vacuum cup'iiactiona This is, however, not absolutely necessary-as \col lapsed' cellular rubber has an irregular surface as theresult of the collapsing of the cells, 'which is rough enough to provide some initial vacuum cup action up to the time that the cells begin to be opened by wear.

The accompanying drawing shows a shoe-sole embodying my invention: Fig. 1 is a perspective view of the sole applied to a shoe; Fig..2 is an enlarged diagrammatic vertical section ofthe sole when new, and Fig. 3 is a; similarV section of the sole after part of it has worn away.

The sole illustrated has a. body I of collapsed closed-cell cellular soft rubber and an under-surface which is indented. When the sole is new, slipping is prevented by the vacuum cup action of the Vindentations 3 in the lower surface shown in Fig. 2. After wear, slipping is prevented by the vacuum cup action of the opened and expanded cells 4 near the wearing surface, as shown in Fig. 3. The cells 5 in the body remain co1- lapsed until they are exposed by wear.

The sole which has been described may be made by utilizing4 the rst part of a method which has been used formaking sponge rubber. This method consists in expanding a mass of rubber compound by means of sodium bicarbonate or a similar blowing agent which is mixed with the compoundbefore vulcanization. During the rst part ofthe vulcanization, the rubber compound is conned in a mold having an internal volume no greater than the volume of the compound'. This prevents any substantial evolution of gas within the rubber compound during the first part of the vulcanization and until the rubber compound has acquired a consistency and tensile strength suiiicient to prevent entrapped gas from rupturing it. During the latter part of the vulcanization, the rubber compound is placed f in a larger mold, On release from the first mold,

or during the nal vulcanization from the larger mold, or at both these times, the mass is expanded by gas produced by the blowing agent, so that, at the end of the vulcanization, there is produced a closed-cell cellular soft rubber article having the shape and size of the second mold.

Since the gas produced from sodium bicarbonate or similar blowing agents is of an unstable character, the gasA is condensed or in some way .chemically eliminated from the cells when the expanded article is cooled, so that it collapses and returnsnearly to the size which the compound had before expansion.

In using this method to make a shoe-sole embodying my invention, the mold used in the first part of the 'vulcanization has a thickness substantially equal to that desired in the shoe-sole. The second mold has a thickness several times as great as that of the first mold and, most desircontained in each cell is eliminated on cooling will be apparent to those skilled in the art. while the above-described specitlc embodiment of my invention is the sole of an ordinary shoe,my inventiorl may, without departing from the spirit thereof as defined in the appended claims, be inf y'after expansion. It is to be understood that, as

conlalnlng almost wholly collapsed closed cells.

2. A shoe sole having'a. tread portion adapted to be exposed by wear comprlsins a ylayer oi.' substantially solid rubber containing almost wholly collapsed closed cells. y

3. A shoe tread comprising a layer adapted to be exposed by wear consistlngvof substantially solid rubber containing almost wholly collapsed closed cells. l

WESIEYLSMITH. 

